Computer security system

Abstract

A computer security system employs a first telephone line for controlling a security unit which connects a second telephone line to the computer. Each authorized user must have a user security unit generating a control signal, such as an audio signal modulated by a pulse signal having a selectable pulse frequency, pulse duration and/or duration between pulses.

It is claimed: 
     
       1. A security system for a computer accessible through a telephone switching network, comprising electrically operable switch means having a normally open circuit for being connected in series with a first telephone line from the telephone network to the computer,   a signal sensing circuit connectable to a second telephone line from the telephone network for responding to a predetermined signal on the second telephone line to operate the switch means to close the normally open circuit, and   a user security unit for generating the predetermined signal and for transmitting the generated signal to the signal sensing circuit through a third telephone line to the telephone network to enable connection of a user terminal to the computer through a fourth telephone line to the telephone network.   
     
     
       2. A security system as claimed in claim 1 wherein the predetermined signal is a continuous periodic signal. 
     
     
       3. A security system as claimed in claim 2 where the predetermined signal has a predetermined frequency. 
     
     
       4. A security system as claimed in claim 1 wherein the user security unit includes a pulse generator for producing a periodic pulse signal, and a modulator connected to the pulse generator for producing the predetermined signal by modulation of an audio signal by the pulse signal; and wherein the signal sensing circuit includes a demodulator for producing the pulse signal from the modulated audio signal, and means for determining a predetermined condition of the pulse signal to operate the switch means. 
     
     
       5. A security system as claimed in claim 4 wherein the predetermined condition of the pulse signal includes a pulse duration. 
     
     
       6. A security system as claimed in claim 4 wherein the predetermined condition of the pulse signal includes a duration between pulses. 
     
     
       7. A security system as claimed in claim 4 wherein the predetermined condition of the pulse signal includes both pulse duration and a duration between pulses.